1. Field of the Invention
The present invention relates generally to semiconductor integrated circuits, and more specifically to the formation of field oxide regions in a semiconductor substrate.
2. Description of the Prior Art
The increase in densities of integrated circuits has raised issues of how to miniaturize components within an integrated circuit, while maintaining the reliability and proper operation of the device. When building a variety of components on one integrated circuit, it is necessary to isolate active areas in the substrate. A common method for isolating active areas is through the formation of field oxide regions. In this process regions of silicon dioxide are selectively formed on the substrate. This is typically known in the art as local oxidation of silicon, or LOCOS.
Several problems are encountered however, with the conventional process of forming field oxide regions. First, LOCOS produces a bird's beak caused by lateral diffusion of the silicon dioxide. This lateral diffusion has the undesirable effect of reducing the size of the active areas within the substrate.
Another problem is a condition known as latchup. Latchup is caused by parasitic devices which are inherent components of any CMOS device. These parasitic components are formed by the various physical regions which make up the CMOS device.
Those skilled in the art will recognize that one technique used to lower the probability of latchup is the formation of a channel stop region. Another possible solution is to form a field oxide region which extends deeper into the substrate. This has the effect of increasing the threshold voltages of the parasitic components. However, when forming a field oxide region that extends deeper into the substrate, the resulting structure becomes more non-planar. This undesirable effect makes further processing steps more difficult.
Therefore, it would be desirable to provide a technique for forming field oxide regions that are more planar with the substrate and extend deeper into the substrate, and that when formed have little or no bird's beak.